Mk1 yaris Immobiliser not responding ?

[Gary mr2]

Hi,  I've got a mk1 yaris 2005  and the car won't start it turns over but won't fire and the security light on th dash doesn't flash got someone to read the codes and it says immobiliser not responding  ? It won't let him talk to immobiliser,  has anyone any ideas I've checked the immobiliser fuse under the bonnet 30a it's fine but replacedit anyway  

[flash22]

try your spare key, has your key fallen apart or had the Battery changed ? iirc the key has a tiny black chip inside it on the mk 1